Method and apparatus for molding composite articles

ABSTRACT

A method of molding a composite article includes providing a first floating mold that has a fluid backing, wherein the fluid defining the fluid backing is stored in a fluid chamber positioned beneath the first floating mold, providing a second non-floating mold that does not include a fluid backing, and sealing the first floating mold to the second non-floating mold to define a molding chamber thereinbetween.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application claims priority to U.S. Provisional PatentApplication No. 60/881,459, dated Jan. 19, 2007. The disclosure of thisapplication is hereby incorporated by reference in its entirety.

TECHNICAL FIELD

The present disclosure relates generally to the manufacture of injectionmolded articles. Such articles can be molded from a polymer thermosetresin or can be composite articles that are articles having a fiberreinforcement lattice within a cured resin matrix. More particularly,the present disclosure relates to a method and apparatus for injectionmolding such polymer and composite articles.

BACKGROUND

Reaction injection molding and resin transfer molding are processeswherein dry fiber reinforcement plys (preforms) may be loaded in a moldcavity whose surfaces define the ultimate configuration of the articleto be fabricated, whereupon a flowable resin is injected, or vacuumed,under pressure into the mold cavity (mold plenum) thereby to produce thearticle, or to saturate/wet the fiber reinforcement preforms, whereprovided. After the resinated preforms are cured in the mold plenum, thefinished article is removed from the mold.

Improvements in the manufacture of injection molded articles aredesired.

SUMMARY

One aspect of the present disclosure relates to a method and anapparatus for manufacturing an injection molded article.

According to another aspect, the present disclosure relates to a methodand apparatus for manufacturing an injection molded article using afirst mold that is a liquid-backed semi-rigid floating mold incombination with a second mold (e.g., a semi-rigid mold or a thinpolymeric sheet), wherein resin may be injected, with the assist ofvacuum, into the plenum created between the two molds.

A variety of advantages of the inventive aspects of the disclosure willbe set forth in the description that follows, and in part will beapparent from the description, or may be learned by practicing theinventive aspects of the disclosure. It is to be understood that boththe foregoing general description and the following detailed descriptionare exemplary and explanatory only and are not restrictive of theinventive aspects claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of this specification, illustrate several aspects of the disclosureand together with the description, serve to explain the principles ofthe inventive aspects of the disclosure. A brief description of thedrawings is as follows:

FIG. 1 is a schematic diagram illustrating a first embodiment of aninjection molding apparatus and method having features that are examplesof inventive aspects in accordance with the principles of the presentdisclosure; and

FIG. 2 is a schematic diagram illustrating another embodiment of aninjection molding apparatus and method having features that are examplesof inventive aspects in accordance with the principles of the presentdisclosure.

DETAILED DESCRIPTION

Reference will now be made in detail to examples of inventive aspects inaccordance with the principles of the present disclosure that areillustrated in the accompanying drawings. Wherever possible, the samereference numbers will be used throughout the drawings to refer to thesame or like parts.

An apparatus 10 embodying examples of inventive aspects in accordancewith the principles of the present disclosure is illustratedschematically in FIG. 1. It should be understood that, while theapparatus and method described herein may be suitable for injectionmolding of boat components, the apparatus and method can be used for themanufacture of any molded article.

Referring to FIG. 1, the injection molding apparatus 10 includes a firstmold section 12 and a second mold section 14. The first mold and thesecond mold sections 12, 14 can be referred to herein as the lower moldand the upper mold sections, respectively. The lower mold section 12includes a semi-rigid mold member 16 that is supported on top of a rigidouter support housing 18. The lower mold member 16 may be sealed againstthe outer housing 18 at its flanges 20. The lower mold member 16 has aninner molding surface 22 having the shape of the outer surface of anarticle 21 to be manufactured.

The outer support housing 18 includes a fluid-tight chamber 24. Thesemi-rigid mold member 16 is supported by a substantiallynon-compressible heat-conductive fluid backing 26 that is located withinthe fluid-tight chamber 24. The semi-rigid mold member 16, since it hasa fluid backing 26, can be referred to herein as the floating moldmember 16. In one embodiment, the floating mold member 16 may be about ⅜of an inch to about ⅝ of an inch in thickness.

The upper mold section 14 also includes a semi-rigid mold member 28. Thefloating mold member 16 works in combination with the semi-rigid moldmember 28 of the upper mold section 14, which mounts over the floatingmold member 16, to form the molding plenum 30 (i.e., molding chamber ormolding cell) thereinbetween. In certain embodiments, the uppersemi-rigid mold member 28 may be a relatively thin, fiberglass moldmember. In one embodiment, the upper semi-rigid mold member 28 may be asthin as ⅛ of an inch. In other embodiments, the upper semi-rigid moldmember 28 may be thicker.

The upper semi-rigid mold member 28 has an inner surface 32 having theshape of the outer surface of the article 21 to be manufactured, whereinthe upper and the lower mold members 28, 16 are configured to shapeopposing outer surfaces of the article 21. The semi-rigid upper moldmember 28 may also define injection port(s) 34 communicating with themolding chamber 30 for injection of resin into the chamber 30, as willbe discussed in further detail below.

In certain embodiments, both the upper mold member 28 and the lowerfloating mold member 16 are capable of slightly flexing when pressurizedresin is injected into the mold chamber 30. In one embodiment, the upperand the lower mold members 28, 16 may be made of sheets of metal. Inother embodiments, the upper and the lower mold members 28, 16 can bemade of other materials such as fiberglass, plastic, reinforced nylon,etc. Preferably, materials that are conveniently and cost-effectivelyfabricated, shaped and reshaped in a pressure chamber in a matter knownto those skilled in the art would be suitable. In this regard, use ofdifferent materials for the mold members 28, 16 may be chosen, forexample, upon the desired characteristics for the mold members (e.g.,thermal conductivity, formability, and usable life), the desiredcharacteristics of the fabricated article (e.g., surface finish andgloss), and/or overall process parameters (e.g., resin injectionpressures, resin cure time and mold assembly cycle time).

Once the upper mold member 28 is placed on top of the floating moldmember 16, a vacuum double seal can be used to hold the upper semi-rigidmold member 28 against the floating mold member 16 during resininjection.

As noted above, to prevent the floating mold member 16 from excessivelydeforming during the molding process, the fluid-chamber 24 is preferablyfilled with the non-compressible liquid 26, such as water. In thisregard, the fluid-chamber 24 preferably includes inlet(s) (not shown)for filling the chamber 24 with the non-compressible liquid 26. Theinlets may be opened and closed by valves as known in the art.

By filling the fluid chamber 24 with the non-compressible liquid 26 andthen sealing the chamber 24 with the floating mold member 16, the liquid26 retained within the chamber 24 provides backing support to thefloating mold member 16 such that deformation of the mold member 16 isresisted. The fluid chamber 24 is completely filled with thesubstantially noncompressible heat-conductive fluid 26 supplied by afluid supply network, and, once the fluid chamber 24 is full, the moldapparatus 10 becomes ready to be used to manufacture articles.

The fluid backing 26 under the lower mold member 16 provides support incompression during resin injection. Since the fluid 26 is substantiallynon-compressible, any force exerted on the floating mold member 16, suchas internal injection pressures, is normally transferred through thefluid 26 to the walls of the rigid outer housing 18. Thus, due to thenon-compressibility of the backing fluid 26, the floating mold member 16may act as a hydraulic system. As will be discussed further below, oncethe resin injection starts, the pressure within the backing fluid 26starts to build up but is maintained at atmospheric pressure through apressure vent 36.

Due to the semi-rigid character of the mold members 16, 28, the moldmembers 16, 28 can dimensionally flex slightly during the injection ofmolding resin as the backing fluid 26 distributes the resultinginjection pressure load across the entire surface of the mold members16, 28. In this manner, the semi-rigid mold members 16, 28 avoid extremestress concentrations on the molding surfaces 22, 32 during injection.Indeed, the slight flexing of the mold members 16, 28 during injectionis believed to further improve or enhance the flow of resin through themold plenum 30.

For the molding apparatus 10 discussed herein, the backing fluid 26 canbe water which may be supplied by a fluid network to the fluid chamber24 through an inlet valve (not shown). Water is generally the preferredfluid since it is inexpensive, readily available and environmentallyfriendly. However, other suitable backing fluids useful over differentoperating ranges (e.g., having higher vaporization temperatures) knownto those skilled in the art may be used. A pressure gauge (not shown)may be employed downstream of the fluid inlet valve to monitor the flowrate of the backing fluid 26 into the chamber 24. To facilitate thefilling and emptying of the chamber 24, the chamber 24 can have a ventthrough which air within the chamber 24 may escape upon the fillingthereof with backing fluid 26. Once filled, the chamber's vent may besealed with a vent valve, thereby imparting requisite rigidity to thelower floating mold member 16. As discussed above, during resininjection, as the pressure in the water builds up, the pressure can beequalized to atmospheric pressure through the pressure vent 36.

Still referring to FIG. 1, the molding apparatus 10 includes a resininjection structure 38 for introducing resin into the molding chamber30. For example, an injection sprue 40 that extends through the uppersemi-rigid mold member 28 is used for injecting resin into the moldingchamber 30, as shown schematically. Preferably, the sprue 40 is placedin fluid communication with a source of resin (e.g., a source of liquidthermoset resin) such that resin can be pumped from the source of resinthrough the sprue 40 into the molding chamber 30. While a single sprue40 has been shown schematically in FIG. 1, it will be appreciated thatmultiple sprues can be provided to provide uniform resin flow throughoutthe molding chamber 30.

As noted, the injection sprue 40 may extend through the upper moldmember 28 to provide a pathway through which a desired type of thermosetresin from a molding fluid supply may be injected under pressure by asuitable injection pump into the mold plenum 30. The number andplacement of such sprues, again, depends upon the configuration anddesired characteristics of the article to be molded, and the flowcharacteristics of the molding resin employed, in a manner known tothose skilled in the art. In this regard, a number of small vents can beprovided between the opposed mold members 16, 28, through which trappedair may bleed to the atmosphere during injection of the molding resininto the mold plenum 30. Alternatively, other, conventional methods ofproviding for the escape of trapped air from the mold plenum 30 may beemployed.

For molding purposes, prior to securing the upper semi-rigid mold member28 to the lower floating mold member 16, to enhance the aestheticappearance of the article 21 to be manufacture, the lower mold member 16may be coated with a layer of gel coat prior to enclosing fibrousreinforcing material within the cell 30. Additionally, barrier coatlayers may also be provided over the layers of gel coat for preventingthe fibrous reinforcing material from printing or pressing through thegel coat layers. An exemplary barrier coat layer may be a layer of vinylester having a thickness of about 0.025 inches. In one embodiment, thegel coat layer can have a thickness of about 0.020-0.024 inches.

Once the fibrous reinforcing material and other desired layers areplaced in the mold chamber 30, the upper mold member 28 is placed overthe floating mold member 16 to enclose the mold chamber 30.

Thereafter, a vacuum assist system 42 is used to saturate the fiberglasswith resin, as will be discussed in further detail below. The resin isinjected with pressure into the molding chamber 30 and a vacuum 42 isused to move resin through the fiberglass. The optimal flow rate atwhich the molding resin is injected is based upon a number of factorswell known to those skilled in the art. Once the mold plenum 30 iscompletely filled with molding resin, the injection ceases. Whether themold plenum 30 is completely filled can be confirmed in a number ofdifferent methods, including visually, via sensors, etc.

As discussed above, as the resin is injected into the plenum 30, thepressure within the backing fluid 26 is preferably maintained atatmospheric pressure. The upper mold member 28 may be flexible enough toallow movement and allow resin to move as well. The upper mold member 28is configured to also allow for the vacuum 42 to draw excess resin outof the part at the end of the cycle to eliminate resin rich areas. Thismay be accomplished by turning off the resin injection structure 38 andonly drawing a vacuum 42.

To optimize the molding process, various devices commonly known to thoseskilled in the art can be employed to provide feedback which can beutilized to adjust different parameters of the molding process, such asthe injection rate, etc., to improve the quality of the molded article21.

It will be appreciated that the molding apparatus 10 can include avariety of additional structures for enhancing the molding process. Forexample, as will be discussed in further detail below, the liquid 26providing the backing to the floating mold member may be heated. Byheating the backing fluid 26, the cure speed of the resin within themolding chamber 30 may be increased so that parts 21 removed from themold can be 97-98% cured. This helps resist shrinkage and provides asmooth finish. Also as mentioned above, the vacuum 42 may be used todraw the resin through the molding chamber 30.

Referring to FIG. 1, the molding process is discussed. After applicationof a release coat, a gel coat, and a skincoat (if desired) to the innersurface 22 of the lower mold member 16, reinforcement material is placedon the inner surface 22 of the lower mold member 16. According to oneembodiment, the reinforcement material may be dry material. Thereinforcement material may include various types of fibrous materialincluding chopped glass fiber, chopped strand mat, cut rovings, wovenrovings, or a combination of these. In certain embodiments, the moldingapparatus 10 may also be used to form molded articles from a curablefiber reinforced composite sheet, optionally, without injecting moldingresin.

Next, other structural members (if desired) may be placed on top of thereinforcement material. Once the semi-rigid upper mold member 28 isvacuum sealed to the floating mold member 16, injection of the resinstarts.

During the injection process, the plenum 30 may communicate with avacuum system 42, as illustrated schematically in FIG. 1, to create avacuum in the molding chamber 30. The vacuum system may include a vacuumpump, as know in the art. The pump reduces the pressure, relative to theambient pressure, in the mold chamber 30. Alternatively, any suitablearrangement can be employed for reducing the pressure in the moldchamber 30 relative to the ambient pressure. After a vacuum has beendrawn in the mold chamber 30, resin is injected through injection ports34 that run through the upper mold member 28 into the mold chamber 30.

Any suitable resin can be employed. The molded fiber reinforced article21 may comprise curable thermoset resin such as unsaturated polyesterresin. Suitable thermosetting resins include acrylic polymers,aminoplasts, alkyd, polyepoxides, phenolics, polyamides, polyolefins,polyesters, polyurethanes, vinyl polymers derivatives and mixturesthereof.

Because of the reduced pressure in the mold chamber 30, resin does nothave to be injected under significant pressure. In certain embodiments,the resin may be injected at a pressure less than 15 psi. The resin cancompletely fill the mold chamber 30, saturating the dry reinforcementmaterial. The vacuum is maintained until the resin is cured. The uppersemi-rigid mold member 28 is then removed from the floating mold member16 to remove the molded article 21.

As discussed above, the molding apparatus 10 can include a variety ofadditional structures for enhancing the molding process. For example,the molding apparatus 10 can include a heating and/or cooling mechanism46 for controlling the temperature of the fluid 26 contained in thefluid chamber 24. Additionally, as noted previously, the fluid chamber24 can include closeable vents for allowing air to be bled from thefluid chamber 24 as the fluid chamber 24 is filled with liquid.Furthermore, the molding chamber 30 can include closeable vents forbleeding resin from the molding chamber 30 once the molding chamber 30has been filled with resin.

As seen in the schematic diagram of FIG. 1, the fluid chamber 24 may bein communication with a fluid backing heating and/or cooling mechanism46. Such a mechanism 46 may comprise a system of heating and/or coolingcoils (not shown) extending within the fluid chamber 24 for regulatingthe temperature of the backing fluid 26, thus the mold chamber 30. Theheating and/or cooling coils can be coupled to an external heater and/orchiller of conventional design of the mechanism 46, as illustratedschematically. As such, the coils operate in conjunction with the heaterand/or chiller 46 to precisely regulate the temperature of the backingfluid 26 and, hence, of the molding chamber 30 throughout the injectionmolding process.

Although the coils are not specifically illustrated in FIG. 1, it shouldbe noted that the thermal conductivity of the backing fluid 26 enablessubstantial design variation with respect to placement of the coilswithin the fluid chamber 24.

In addition, while the mold members 16, 28 of the exemplary apparatus 10are shown in FIG. 1 as being of relatively uniform thickness, theefficiency with which mold temperature may be controlled under thepresent process permits the use of variable-thickness members, as may bedesirable, for example, when providing the finished article withreinforcement ribs.

To the extent that the backing fluid 26 with which the chamber 24 isfilled is supplied at a temperature different from the desired processtemperature, upon subsequent heating or cooling of the fluid backing 26to the desired temperature, any resulting thermal expansion thereof canbe accommodated by the pressure vent 36, thereby preventing distortionand/or extreme stress on the mold members 16, 28.

When the fluid chamber 24 is being filled, the chamber 24 is sealed withits respective valve and the heater and/or chiller 46 are operated tobring the chamber 24 to the desired process temperature. The fluid inletvalve is thereafter closed to isolate the fluid chamber 24 from thefluid supply network.

The temperature of each mold member 16, 28 can be regulated viaoperation of the heater and/or chiller 46 to thereby provide an optimumcure rate with which to obtain the desired surface finish and/or otherdesired characteristics of the finished article 21, or to otherwiseoptimize the molding process.

The heater and/or the chiller units 46 are operated to bring the moldchamber 30 to the desired process temperature. Typically, the fluidchamber 24 is filled with backing fluid 26 prior to forming the firstmolded article and topped-off with backing fluid 26 as necessary beforethe subsequent molding steps in order to maintain the fluid chamber 24in a completely filled state. The temperature of the backing fluid 26may be adjusted before or after engaging the mold members 16, 28 to formthe composite article. The backing fluid 26 provides precise control ofthe temperature of the mold members 16, 28 and enables the temperatureof the mold chamber 30 to be varied according to the optimum curetemperature and cure rate for the reinforced composite article.

In certain embodiments, a backing fluid pump (not shown) can also beprovided to increase the pressure in the fluid chamber 24 by pumpingfluid into the chamber 24 after injection is complete. If the pressurevent 36 is closed, this increases the pressure in the fluid chamber 24which effectively increases the pressure in the mold plenum 30. Thismight be desirable, for example, after the mold is filled in order tospeed up the curing process of the resin to increase the cycle time. Inone embodiment, using the process described herein, the entire processto mold a composite article may be less than about 90 minutes. In oneembodiment, the injection start to cure time may be about 60 minutes.

Preferably, the fluid filled chamber 24 provides excellent thermalconductivity which permits superior mold temperature control. A floatingmold member 16 according to the disclosure provides a stable andcontrollable mold surface temperature which permits molding to beperformed without needing to compensate for ambient conditions. Thecontrolled temperature ranges permit the resin flow to be much faster incycle times and provide the added bonus of the chemical reaction'soptimal control limits being unaffected by the ambient temperatureranges that can otherwise effect production rates. Thus, such aclosed-mold system 10 creates new controls and predictability in theproduction of molded parts as well as improved cosmetics.

In using the molding apparatus 10 illustrated in FIG. 1, moldingdifferently configured parts may be as simple as removing one set ofmold members 16, 28 and replacing them with a differently configuredset.

Some benefits of the floating mold member 16 and the semi-rigid moldmember 28 that is mounted on the floating mold member 16 areflexibility, reduced cost, speed to market and increased closed moldingperformance. For example, when a part design is changed, rather thancreating new molds and obsoleting current molds, or performing expensivemold modifications, the mold members 16, 28 may simply be changed out.

One example application for the molding apparatus 10 of the presentdisclosure is for molding of boat decks and hulls. The mold members 16,28 can be changed to create different parts whenever needed.

Besides of the use of the closed-loop temperature regulating system, thecontainment of the non-compressible fluid 26 remains an advantageousfeature of the present apparatus 10. Since the fluid 26 is confined andbecause the fluid 26 is noncompressible, it serves to strengthen thefloating mold member 16. By using the fluid 26, the floating mold member16 can be formed in a very thin layer. Consequently, heat transfercontrol of the molded part may be enhanced and the mold members 16, 28can be formed more easily and less expensively. Preferably, each moldmember 16, 28 can be formed from a highly thermally-conductive material.The relatively large volume of fluid 26, such as water, also provides arelatively stable temperature environment, since it resists rapidfluctuations in temperature which can adversely affect the molded part.

Exemplary fluid-backed, closed-loop temperature regulated systems usingfloating mold members are disclosed in U.S. Pat. Nos. 6,143,215,6,623,672, and 6,994,051, which are incorporated herein by reference intheir entirety.

Referring now to FIG. 2, another embodiment of a molding apparatus 110and method having features that are examples of inventive aspects inaccordance with the principles of the present disclosure is shown. Themolding apparatus 110 and method illustrated in FIG. 2 is similar tothat shown in FIG. 1. However, rather than using a semi-rigid flexibleupper mold 28, a relatively thin sheet 128 (e.g., a polymeric sheet suchas a nylon sheet, etc.) may be used to enclose the top side of thefloating mold member 16. In one embodiment, the sheet 128 may be about 5mils to 25 mils in thickness. In another embodiment, the sheet 128 maybe about 7 mils to 20 mils in thickness. In yet another embodiment, thesheet 128 may be about 8 mils in thickness.

The sheet 128 may be reused or be a throw-away part and may besubstantially more cost-effective to manufacture than a harder mold suchas a semi-rigid mold 28. Further, the thin nature of the sheet 128allows more resin to be pulled from the part 21 thereby reducing costs.Moreover, the process can allow thinner, lighter-weight parts to bemanufactured. The apparatus 110 and method shown in FIG. 2 may speed upprototyping and allow the use of more exotic molding materials, such asepoxies.

As used herein, a mold member may be referred to as a “semi-rigid” or a“semi-flexible” member if the mold member is capable of slightly flexingwhen pressurized resin or other molding material is injected into themold chamber formed by at least one surface of the mold member.

With regard to the foregoing description, it is to be understood thatchanges may be made in detail, especially in matters of the constructionmaterials employed and the shape, size and arrangement of the partswithout departing from the scope of the present disclosure. It isintended that the specification and depicted aspects be consideredexemplary only.

1. A method of molding a composite article comprising: providing a firstfloating mold that includes a fluid backing, wherein the fluid definingthe fluid backing is stored in a fluid chamber positioned beneath thefirst floating mold; providing a second non-floating mold that does notinclude a fluid backing; and sealing the first floating mold to thesecond non-floating mold to define a molding chamber thereinbetween. 2.A method according to claim 1, wherein resin is injected into themolding chamber defined between the first and second molds.
 3. A methodaccording to claim 2, further comprising keeping the fluid pressure inthe fluid chamber at atmospheric pressure during the injection of theresin.
 4. A method according to claim 1, wherein the non-floating moldis manufactured from a semi-rigid material.
 5. A method according toclaim 4, wherein the non-floating mold is manufactured from fiberglass.6. A method according to claim 4, wherein the non-floating mold ismanufactured from flexible metal.
 7. A method according to claim 1,wherein the non-floating mold is manufactured from a polymeric sheet. 8.A method according to claim 7, wherein the polymeric sheet includesnylon.
 9. A method according to claim 7, wherein the polymeric sheet hasa thickness of about 8 mils.
 10. A method according to claim 2, furthercomprising using vacuum to draw resin through the molding chamber.
 11. Amethod according to claim 2, wherein the fluid in the fluid chamber isheated.
 12. A method according to claim 1, further comprising providingfiber glass reinforcement material in the first floating mold prior tosealing the first floating mold to the second non-floating mold.